Constitutive overexpression of cellobiohydrolase 2 in reveals its ability to initiate cellulose degradation.

Cellulose degradation results from the synergistic effect of different enzymes, but which enzyme is involved in the initial stage of cellulose degradation is still not well understood. Cellobiohydrolase 2 (CBH2) attached to the conidial surface is possibly associated with the initial stage. However, its specific mechanism is still incompletely known. This study explored the potential role of CBH2 in initiating cellulose degradation using a constitutive overexpression strategy. First, the CBH2-overexpression strains Qgc2-5 and Qrc2-40 were constructed using the constitutive promoters P and P, respectively. It was found that was expressed at a high level under the glucose conditions and was significantly higher than that of the parental strain QM9414 at the early stage of 29 h when cellulose was used as the carbon source. Particularly, the constitutive overexpression of caused the strong expression of major cellulase-encoding genes (, and ) and the rapid decomposition of cellulosic material. Meanwhile, the scanning electron microscope showed that the groove-like structure of the cellulose surface was eroded seriously owing to CBH2 overexpression, which caused the cellulose surface to be smooth. These results showed that the overexpression of CHB2 caused the major cellulase enzymes to be expressed and contributed to cellulose degradation, showing the potential role of CBH2 in the initial stage of the cellulose hydrolytic process.